【洛谷 P2464】[SDOI2008]郁闷的小J（线段树）

题目链接

这题我很久之前用分块写过，没写出来。。

今天又看到了，于是下决心把这题做出来。

这次我用线段树写的，直接对每本书的编号Hash一下然后离散化然后各建一棵线段树，维护当前编号在某个位置有没有书，就行了。

为了卡空间，我用了\(vector\)，同时指针建树，结构体里不保存当前节点维护的区间，区间作为参数递归，这样就能过了，空间复杂度应该是\(O(N+M\ log\ N)\)。

另外Hash的边界搞大一点，第一次只弄了10W 80分，改成100W就A了。

#include <iostream>
#include <cstdio>
#include <vector>
#define re register
using namespace std;
inline int read(){
    int s = 0, w = 1;
    char ch = getchar();
    while(ch < '0' || ch > '9') { if(ch == '-') w = -1; ch = getchar(); }
    while(ch >= '0' && ch <= '9') { s = s * 10 + ch - '0'; ch = getchar(); }
    return s * w;
}
const int MAXN = 100010;
int num;
struct Seg_Tree{
    int sum;
    Seg_Tree *l, *r;
    Seg_Tree() { l = NULL; r = NULL; sum = 0; }
    void pushup(){
        sum = 0;
        if(l != NULL) sum += l->sum;
        if(r != NULL) sum += r->sum;
    }
    void Add(int c, int p, int L, int R){
        if(L == R){
          sum += c;
          return;
        }
        int mid = (L + R) >> 1;
        if(p > mid){
          if(r == NULL)
            r = new Seg_Tree;
          r->Add(c, p, mid + 1, R);
        }
        else{
          if(l == NULL)
            l = new Seg_Tree;
          l->Add(c, p, L, mid);
        }
        pushup();
    }
    int Ask(int L, int R, int wl, int wr){
       int ans = 0;
       if(L >= wl && R <= wr) return sum;
       if(L > wr || R < wl) return 0;
       int mid = (L + R) >> 1;
       if(l != NULL) ans += l->Ask(L, mid, wl, wr);
       if(r != NULL) ans += r->Ask(mid + 1, R, wl, wr);
       return ans;
    }
};
vector <Seg_Tree> tree;
int n, m, v[MAXN * 10], id[MAXN * 10];
int getHash(int x){
    int hash = x % 1000000;
    if(!v[hash]) v[hash] = x;
    else while(v[hash] != x && v[hash]) hash = (hash + 233) % 10000;
    return hash;
}
int a, b, c;
int w[MAXN];
char ch;
int main(){
    tree.push_back(Seg_Tree());
    n = read(); m = read();
    for(re int i = 1; i <= n; ++i){
       w[i] = read();
       re int hash = getHash(w[i]);
       if(!id[hash]) id[hash] = ++num, tree.push_back(Seg_Tree());
       tree[id[hash]].Add(1, i, 1, n);
    }
    for(re int i = 1; i <= m; ++i){
       do{
         ch = getchar();
       }while(ch != 'C' && ch != 'Q');
       if(ch == 'C'){
         a = read(); b = read();
         re int hash = getHash(w[a]);
         tree[id[hash]].Add(-1, a, 1, n);
         hash = getHash(b);
         if(!id[hash]) id[hash] = ++num, tree.push_back(Seg_Tree());
         tree[id[hash]].Add(1, a, 1, n);
         w[a] = b;
       }
       else{
         a = read(); b = read(); c = read();
         re int hash = getHash(c);
         if(!id[hash]) id[hash] = ++num, tree.push_back(Seg_Tree());
         printf("%d\n", tree[id[hash]].Ask(1, n, a, b));
       }
    }
    return 0;
}